1. Field of the Invention
The present invention relates to a TV camera lens device, and more particularly to a technique of controlling a TV camera lens which is capable of forming an optical system in which a macro-shooting can be performed by moving the whole of a master lens group or a part thereof along an optical axis.
2. Description of Related Art
In a zoom lens applied in a broadcast TV camera, one of the whole of a master lens group in a taking lens system and a part of the master lens group is moved forward and backward along the optical axis to adjust the flange back length, thereby forming a sharp image of an object on a picture screen. Japanese Patent Publication Nos. 58-1401 and 60-46405 disclose TV camera lenses in which the master lens group, which is the identical master lens group that is moved forward and backward along the optical axis to adjust the flange back length, is moved forward and backward along the optical axis to form an optical system for the macro-shooting.
Further, such TV camera lenses are known where the master lens group is divided into two groups including a macro lens group, which is moved and controlled during the macro-shooting, and another lens group for adjusting the flange back length, which is moved and controlled during the flange back length adjustment. During the macro-shooting, the macro lens group, which is a part of the master lens group, is moved and controlled. During the flange back length adjustment, the lens group for adjusting the flange back length, which is a part of the master lens group, is moved and controlled.
In general, a rotary adjustment knob is provided on one side of the mount frame (the right side viewed from the front, i.e. the left side of a user) so that rotational force of the adjustment knob can be transmitted to a master lens driving mechanism in a lens mount via a power transmission mechanism such as an assembly of gears. If the user turns the adjustment knob by hand, an image formation position of the TV camera lens can be finely adjusted and the macro-shooting can be performed.
In the TV camera lens in which the master lens group is moved to perform both the flange back length adjustment and the macro-shooting, however, since the normal shooting is usually performed after the flange back length adjustment is completed, and a knob or the like is operated on demand to changeover to the macro-shooting, there is a problem that the operation becomes troublesome. Further, it is difficult to correctly return the master lens group to the initially-adjusted position of the proper flange back length when the shooting is switched from the macro-shooting to the normal shooting.
Similarly, also in the TV camera lens in which the macro lens group or the lens group for adjusting the flange back length, both of which are parts of the master lens group, is moved and controlled, respectively, to perform the macro-shooting or the flange back length adjustment, it is necessary to correctly return the macro lens group to the initially-adjusted position, particularly to the normal shooting position in the balance with the flange back length adjustment, when the macro lens group is moved to a macro-shooting position or a normal shooting position.
Furthermore, since it is desirable that the flange back length is precisely adjusted, the flange back length is frequently adjusted every time the shooting is performed. As for the macro position, there are such characteristics that a standard macro position is preset on manufacturing and the adjustment in focusing can be performed by a zoom lens.